We need an energy plan that adds up

Wednesday, April 29, 2009

The problem with most discussions about ways to save energy is that they're based on incorrect information and it's time to have a serious look at what can and can't be done, writes David MacKay

The public discussion of energy options tends to be intensely emotional, polarized, mistrustful, and destructive. Every option is strongly opposed: the public seem to be anti-wind, anti-coal, anti-waste-to-energy, anti-tidal-barrages, anti-carbon-tax, and anti-nuclear.

We can't be anti-everything! We need an energy plan that adds up. But there's a lack of numeracy in the public discussion of energy. Where people do use numbers, they select them to sound big, to make an impression, and to score points in arguments, rather than to aid thoughtful discussion.

I would like to help people have honest and constructive conversations about energy. We need to understand how much energy our modern lifestyles use; we need to decide how much energy we would like to use in the future; and we need to choose where we will get that energy from.

I think it sheds light on the scale of the energy problem if we discuss all forms of energy in simple personal units. In my book, Sustainable Energy - without the hot air, I express everything in kilowatt-hours. One kilowatt-hour (kWh) is the electrical energy used by leaving a 40-watt bulb on for 24 hours. The chemical energy in the food we eat to stay alive amounts to about 3 kWh per day. Taking one hot bath uses about 5 kWh of heat. Driving an average European car 50km uses 40 kWh of fuel. With a few of these numbers in mind, we can start to evaluate some of the recommendations that people make about energy. Take, for example, the idea that one of the top ten things you should do to make a difference to your energy consumption is to switch off your cell-phone charger when you are not using it. The truth is that leaving a phone charger switched on uses about 0.01 kWh per day - one hundredth of the power consumed by a lightbulb. Switching the phone charger off for a whole day saves the same energy as is used in driving an average car for one second. Switching off phone chargers is like bailing the Titanic with a teaspoon. I'm not saying you shouldn't switch it off - do switch if off, but please realise, when you do so, what a tiny fraction it is of your total energy footprint.

In total, the European lifestyle uses 125 kWh per day per person for transport, heating, manufacturing, and electricity. That's equivalent to every person having 125 lightbulbs switched on all the time.

And most of this energy today comes from fossil fuels. What are our post-fossil-fuel options?

Among the energy-saving options, two promising technology switches are the electrification of transport (electric vehicles can be about four times as energy-efficient as standard fossil-fuel vehicles) and the delivery of winter heating and hot water by electric-powered heat pumps (which can be four times as energy-efficient as standard heaters).

Among all the energy-supply technologies, the three with the biggest potential today are wind power, nuclear power, and solar power – especially solar power in sunnier countries, which Britain could buy via a European electrical super-grid (yet to be built).

As a thought-experiment, let's imagine that technology-switches and lifestyle changes manage to halve British energy consumption to 60 kWh per day per person. How big would the wind, nuclear, and solar facilities need to be to supply this halved consumption? Here is the scale that is required if (for simplicity) we wanted to get one third from each of these sources: we would have to build wind farms with an area equal to the area of Wales; we would have to build 50 Sizewells of nuclear power; and we would need solar power stations in deserts covering an area twice the size of Greater London.

Of course I'm not recommending this particular mix of options; there are many mixes that add up; and a more detailed story would discuss other technologies such as 'clean coal' with carbon capture and storage (as yet, unproven); and energy storage systems to cope with fluctuations of supply and demand.

What about tidal power? What about wave power? What about geothermal energy, biofuels, or hydroelectricity? In a short article, I can't discuss all the technology options. But the sober message about wind and solar applies to all renewables: all renewables, much as I love them, deliver only a small power per unit area, so if we want renewable facilities to supply power on a scale at all comparable to our consumption, those facilities, whether centralized or decentralized, must be big.

Whatever mix you choose, if it adds up, we have a very large building task. The simple wind/nuclear/solar mix I just mentioned would involve roughly a one-hundred-fold increase in wind power, and a five-fold increase in nuclear power; the solar power in deserts would require new long-distance cables connecting the Sahara to Surrey, with a capacity 25 times greater than the existing England-France interconnector.

It's not going to be easy to make a energy plan that adds up; but it is possible. We need to get building.

David MacKay is a professor in the Department of Physics at the University of Cambridge.

Our viable energy futures are discussed in detail in the forthcoming edition of Public Service Review: Science and Technology